1. Field of the Invention
This invention relates to a zoom lens suitable for an electronic imaging apparatus, such as a video camera or a digital camera, in which a slim design relating to a depth and a wide-angle design of the zoom lens have been realized, and to the electronic imaging apparatus having the zoom lens.
2. Description of Related Art
Recently, as cameras for the next generation of an alternative to silver halide 35 mm film (135 format) cameras, special attention has been devoted to digital cameras (electronic cameras). Such digital cameras have come to have many categories in a wide range from a high-function type for business use to a popular potable type. In particular, in the popular portable type, cameras which are slim in depth and easy for use have come to be demanded. In addition, cameras which have high image quality and wide angles of view are required.
A thickness extending from the most object-side surface of an optical system to an imaging plane constitutes the greatest obstacle to a reduction in depth of a camera. In particularly, in a zoom optical system, this thickness offers an obstacle. Thus, the slim design technique of a camera body adopting a collapsible lens barrel has been chiefly used in recent years. The collapsible lens barrel is constructed so that the optical system protrudes from the front side of the camera body in photography, but it is incorporated in the camera body when the camera is carried. Optical systems in which the collapsible lens barrel is used and the slim design is effectively achieved are set forth, for example, in Japanese Patent Kokai Nos. Hei 11-194274, Hei 11-287953, and 2000-9997.
Each of the optical systems described in these publications includes, in order from the object side, a first lens unit with negative refracting power and a second lens unit with positive refracting power so that when the magnification of the optical system is changed, both the first lens unit and the second lens unit are moved.
Recently, a new electronic imaging apparatus has been proposed. This electronic imaging apparatus has the feature that there is no rising time (lens shifting time) required to bring the camera into a working state as in the collapsible lens barrel. Such a feature is also favorable for water and dust proof. In order to make a camera extremely small in depth, the optical system of the electronic imaging apparatus of this type is constructed so that the optical path (optical axis) of the optical system is bent by a reflecting optical element such as a mirror or a prism. Specifically, the most object-side lens unit of the optical system is fixed and the reflecting optical element is provided therein. The optical path running behind this lens is bent in a longitudinal or lateral direction of the camera body. By doing so, the smallest possible dimension of the depth is obtained.
In this case, in order to ensure the angle of view of a certain extent, a diverging surface is necessarily provided on the object side of the reflecting surface of the reflecting optical element.
Further, in order to minimize the production of distortion due to the diverging surface, a negative meniscus lens with a concave surface facing the image side of the reflecting optical element is placed.
Still further, in order to achieve path bending in a state where a succeeding lens system is kept to small size, it is necessary to keep an optical effective surface of the reflecting optical element, such as a prism or a mirror, to a minimum.